1. Field of the Invention
This invention relates to electrical-output optical image sensors, and particularly to efficient sensors having high imaging resolution, suitable for resolving views subtending several thousand picture elements in each direction.
2. Prior Art Problem
Until recently, it did not appear feasible to make an electrical-output optical image sensor having preferably very high imaging resolution, as would be required for purposes of remote sensing, mapping, surveillance and tracking, and also having very good quantum efficiency, as would also be preferred for such purposes. There were some high resolution television camera tubes of the "Vidicon" type, developed for such purposes as reproduction of drawings and documents, which could provide excellent imaging resolution but which had very poor quantum efficiency. Conversely, there were sensitive and efficient television camera tubes of other types, but these lacked the desired high imaging resolution. There have recently been developed several solid-state discrete-element electro-optical image sensors which are very compact and have good quantum efficiency, but have only modest imaging resolution, for designs having a tolerable production yield. In addition, these devices are small, light, rugged, long-lived and able to operate using only small amounts of power; these characteristics are very attractive. Recently, therefore, there has been a considerable effort to achieve the desired combination of high total imaging resolution and good quantum efficiency by arraying considerable numbers of such solid-state electro-optical sensors as modules in the focal plane of optical instruments, to add their individual imaging resolutions while retaining their quantum efficiency.
Provision of such a focal plane array presents a design dilemma: first, it is difficult, and probably impractical to produce a solid-state electro-optical image sensor module in which the imaging capability extends all the way to the physical lateral boundaries of the device, due to requirements for space for support and electrical connections, and because of dimensional constraints on the scribing and separating of the module from its parent wafer or substrate. Second, it is difficult to devise a modular array which can be reliably assembled and readily repaired, as required for a high probability of manufacturing yield, unless a reasonable fraction of the periphery of each module is available for mechanical bonds and electrical connections and interconnections. And third, it is undesirable, in many applications, that the total field of view of the sensor array be broken up into an array of non-contiguous fields of view of the individual imaging sensor modules, separated by bars of blindness representing the image-insensitive peripheries of the individual modules and the regions dedicated to bonds, connections and interconnections. It is clear that alleviation of any one of these difficulties, in a direct sense, leads to exacerbation of the other two. It is also clear that thus arraying other kinds of electro-optical imaging sensors, such as television camera tubes, would present essentially the same design dilemma, since their imaging capabilities also do not extend to the lateral boundaries of their envelopes.